Looking at internal pictures of an Aleph J, the Gate resistors are nowhere near the mosfets. The Source resistors are right there with the fets though.
Noticed how NP can also make electrons go on tight 90 deg. corners in his pcb tracks?
http://6moons.com/audioreviews/firstwatt3/alephj.html
Noticed how NP can also make electrons go on tight 90 deg. corners in his pcb tracks?
http://6moons.com/audioreviews/firstwatt3/alephj.html
Robert,
I was unable to see your photos until I disable my firewall and anti-sypware.
I made two sets of ZenV3. The 20KHz output is very similar to what you've got. So it is absolutely normal to have the round-corners.
Nevertheless, I'm pretty happy with the result considering the simplicity of the circuit and the superb sound quality.
I think it is a common problem with MOS FET that caused by the Gate-Source and Gate-Drain capacitances. The 221 ohm resistor at the Gate together with the Gate-Source capacitance will form a RC circuit. Worse of all is that the Gate-Drain capacitance will provide negative feedback path feeding some of the output back to the gate.
That is why although the Gate-Source resistance is very high, we still need a low impedance source to drive a MOS FET so that we can charge the G-S cap quickly and drain away the feedback signal from the G-D cap.
If you can provide a very low impedance signal source, the output may look better. I think you can't do much to improve Zen5.
Zen V9 may provide a better square wave output as the input is isolated from the output.
Could somebody having a ZenV9 publish a 20KHz output photo for comparison?
You made very nice cases.
One suggestion though:
It will increase the efficiency of your heat sinks if the fins are installed vertically. It is too late to say that now, but may be useful when you are making another one (ZenV9 may be?).
I was unable to see your photos until I disable my firewall and anti-sypware.
I made two sets of ZenV3. The 20KHz output is very similar to what you've got. So it is absolutely normal to have the round-corners.
Nevertheless, I'm pretty happy with the result considering the simplicity of the circuit and the superb sound quality.
I think it is a common problem with MOS FET that caused by the Gate-Source and Gate-Drain capacitances. The 221 ohm resistor at the Gate together with the Gate-Source capacitance will form a RC circuit. Worse of all is that the Gate-Drain capacitance will provide negative feedback path feeding some of the output back to the gate.
That is why although the Gate-Source resistance is very high, we still need a low impedance source to drive a MOS FET so that we can charge the G-S cap quickly and drain away the feedback signal from the G-D cap.
If you can provide a very low impedance signal source, the output may look better. I think you can't do much to improve Zen5.
Zen V9 may provide a better square wave output as the input is isolated from the output.
Could somebody having a ZenV9 publish a 20KHz output photo for comparison?
You made very nice cases.
One suggestion though:
It will increase the efficiency of your heat sinks if the fins are installed vertically. It is too late to say that now, but may be useful when you are making another one (ZenV9 may be?).
Hi,
my discussion with Babowana has brought to my attention the possibility that instead of a single pole roll off due to the gate resistor Rgate*Ciss/Cog the long leads from gate resistor to FET gate may have sufficient inductance to form a two pole roll off at a much lower frequency. The new time constants being based on Rgate*Ciss/Cog + Lleads*Ciss/Cog.
Could this be a factor for the rolled off extreme treble?
Maybe oscillation is not a concern with NP's topology.
my discussion with Babowana has brought to my attention the possibility that instead of a single pole roll off due to the gate resistor Rgate*Ciss/Cog the long leads from gate resistor to FET gate may have sufficient inductance to form a two pole roll off at a much lower frequency. The new time constants being based on Rgate*Ciss/Cog + Lleads*Ciss/Cog.
Could this be a factor for the rolled off extreme treble?
Maybe oscillation is not a concern with NP's topology.
AndrewT said:
Once I have made my own capacitor of about 5-10pF with twisted wires of about 60mm length (thanks to Papa’s tip . . .). Based on this experience, I presume that, even if the long leads of the gate and drain (separated each other) create a capacitance, the value would be ignorable low compared with the input capacitance of the MOSFET.
By the way . . . I am with RoboMan (post#45).
RoboMan said:
Humm... Lots of topics...
Re: pictures/AV/firewall stuff:
The pictures should not have any viruses, etc. in them. While I admit that the
PC based O-Scope is running MS, I do not connect it to the Internet. I did
transfer (via sneaker net) the images to a Linux box (that is connected to the
Internet - Linux boxes being more secure than MS boxes), to convert the
images to .jpg's and upload them. I guess that is a long way of saying that
I don't think the pics could have viruses, etc. in them. But if I'm wrong, please
let me know.
Re: Zen 3, square waves with rounded corners:
Thanks for the info. I noticed that in some of the projects that
Babowana has on his website show similar traces. It was also interesting
that some of the traces that Babowana captured of lower freq. square waves
(say 50Hz or so) have a trapazoidal shape, where the leading edge overshoots
the target. I checked and mine does the same thing...
I have an X150 that uses the same MOSFETs. I haven't tested it yet, but
I would bet that Nelson has it making perfect 20kHz square waves. I'll verify
that, but if I'm right, I wonder how Nelson gets around this problem?!?!
And thinking of more traces and testing, I built another Zen 5 board for
workbench testing (instead of goofing with the amps that are built and
working). I cannot tell any difference in the traces between the test
board and the "production" boards.
I tried connecting the gate resistors directly to the gates. There was no
noticable improvement. I think this supports the MOSFET capacitance
issues you mention.
I measured the capacitance of the Dale resistors that I used. I was
surprised to find the the 220 ohm 1/2W gate resistors measured 70pf,
while the 47.5K ohm 1/2W feedback resistors measured .33pf.
I tried measuring the capacitance of misc. lengths of misc. gauge
wire that I used, but I was unable to measure any capacitance.
Re: signal source:
I'll need to look for the output impedance of the signal generator I'm
using. As far as music goes, I'm driving the Zen 5's with a Pass
Labs X-1 preamp, which has an output impedance of 200 ohms.
Re: cases:
Thanks about the cases. They match our furniture, and I really like them
too.
Re: heatsinks:
I got tired of fighting the heat, so I went and got a couple of "wall wart"
type of power supplies that have an adjustable DC voltage switch and
supply an amp of current. Then I got some of the quitest 12VDC, 120mm
fans I could find, and wired them to the supply. I turned the supply down to
7.5V and set 2 fans on the big heat sinks (the "top" of the box). You cannot
hear the fans when you ears are 6" from them. I wired the supply to the amp's
switch so the fans turn on with the amp.
BTW, this has made a HUGE difference in the sound quality of the amp. I
think the voltage would fluctuate too much (due to changes in temps) without
the fans. With the fans, the DC offset and the bias current vary about 25%
of the amount they varied without the fans. I was also able to increase the
bias current to 2.5 amps (and nothing has blown yet).
Re: new projects:
I probably will do more amp projects, but not yet as I'm still learning from
this one!!!
Thanks a bunch (and to everyone),
Robert
against the 90 deg corner wall . . . heheaudiorob said:
Re: pictures/AV/firewall stuff:
Oh, that is the problems of how this forum works and my settings. Nothing to do with your pictures.
Re: signal source:
I suppose you drove your Zen5 directly with the Sig Gen. Since you have the X-1 preamp ready, why not drive Zen5 through X-1 and see.
The Zen needs a really low impedance source.
audiorob said:
My that amp has an input coupling cap forming a RC network with a R referring to the ground. When I give the input a square wave signal (e.g.50Hz), the network sees the initial input voltage 100%, and then, the cap and the R share the input voltage time after time. That is the reason of the slope on the top part of the responding square wave. If I reduce the size of either the cap or R, the slope increases, indicating the low frequency rolloff is getting faster. And, the shape of the slope (not exactly linear to the microscope eyes) depends on the character of RC time constant.
. . . just my poorly-polished interpretation . . .
AndrewT said:
Hi,
I do not know further details than in post #53.
I just like to simplify and apply for a simple engineering -- my way.
The input RC network is a leading network.
At fCL (critical low frequency, -3dB), the phase angle is about +45 deg.
At frequency of 0.1fCL, about +84 deg.
At frequency of 0.01fCL, almost +90 deg.
These are with one pole . . .
AndrewT said:
I will interpret the falling horizontal slope on the square wave as a response fall off indicator instead of phase indicator. It does not show phase shift. A rising horizontal slope will indicator increase in low frequency response (or relatively a decrease in high frequency). You can try it with a preamp that having tone controls.
If you want to measure phase shift you have to include the input signal and compare side by side with the output signal. That means you'll need a dual traces oscilloscope, synchronized to one of the signal.
The horizontal line of a square wave respresents the low frequency response and the vertical line represents the high frequency response. You are right that the slope is more sensitive than measuring the real responses (e.g. by a sinewave).
Nelson Pass said:
Quantum electrodynamics teaches that an electron arrives
at it destination through the "sum of all paths" approach,
with some of the electron cutting across the corner and
some of it by way of Andromeda.
Yes...also remember these aren't ordinary electrons but Pass electrons in the Aleph Dimension and will always make 90 deg corners. Maverick Aleph electrons that find their way to Andromeda must go through dark matter, of low electron density, where they enslave ordinary electrons to get across lightyears of space and time. They'll miss the party unless these maverick electrons modulate light as carrier and will travel at lightspeed.
Just like gate resistors placed right at the threshold, >90 deg copper traces at corners are IMO over rated.
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